Metallurgical coke produced by coal carbonized in a coke oven is generally used in the operation of a blast furnace. In recent years, from the viewpoint of improving the reactivity of coke, there has been known a technique for using metallurgical carbon iron composite produced by carbonizing a mixture of coal and iron ore in the operation of a blast furnace. Carbon iron composite can increase the CO2 reactivity of coke in the carbon iron composite by the catalytic effect of reduced iron ore and can decrease the percentage of a reducing material as a result of a decrease in thermal reserve zone temperature.
Studies have been carried out on a technique for carbonizing a carbon-containing substance such as coal, and an iron-containing substance such as iron ore, in a common chamber coke oven to produce carbon iron composite, for example, a) a method for feeding a mixture of coal and iron ore fines into a chamber coke oven or b) a method for cold-forming coal and iron ore at room temperature and feeding the formed product into a chamber coke oven (see, for example, Fuel Society of Japan, “Kokusu Gijutsu Nenpou (annual report on coke technology),” 1958, p. 38).
However, since conventional coke ovens are constructed of silica stone bricks, iron ore in a chamber coke oven can react with the main component of the silica stone bricks, silica, to form low-melting-point fayalite, causing damage to the silica stone bricks. Thus, a technique for producing carbon iron composite in a chamber coke oven has not been industrially employed.
As a substitute for a method for producing coke in a chamber oven, a method for continuously producing formed coke has been developed. In the method for continuously producing formed coke, a vertical shaft furnace constructed of chamotte bricks in place of silica stone bricks is used as a carbonization furnace. Coal is cold-formed in a predetermined size and fed into a vertical shaft furnace. The briquettes are carbonized by heating with a circulating heating gas to produce formed coke. It has been demonstrated that coke having a strength comparable to that of coke produced with a conventional coke oven can be produced even by using a large amount of naturally abundant and inexpensive non- or slightly-caking coal.
One known method for continuously producing formed coke is characterized in that a top gas of a vertical carbonization furnace is utilized as a coolant gas into a lower portion of a cooling chamber directly coupled to a carbonization chamber of the vertical carbonization furnace. Most of the gas passing through the cooling chamber is exhausted from an upper portion of the cooling chamber and supplied as a heating gas to an inlet in an intermediate portion of the carbonization furnace (see, for example, Japanese Examined Patent Application Publication No. 56-47234). This method requires three gas inlets (an intermediate portion of the carbonization chamber, a lower portion of the carbonization chamber, and a lower portion of the cooling chamber) and one gas outlet (an upper portion of the cooling chamber), which makes the equipment complicated. Sensible heat generated by the cooling of high-temperature coke after carbonization is recovered with a gas and reused by supplying the heat to an intermediate portion of the carbonization furnace. However, there is a problem of heat loss. To simplify the equipment, another method for producing formed coke is disclosed which does not require the removal of gas from an intermediate portion of a vertical carbonization furnace (see Japanese Unexamined Patent Application Publication No. 52-23107). In accordance with that method, coke after carbonization is cooled in a water tank instead of using a gas. One of characteristics of carbon iron composite is that iron ore can be reduced to metallic iron during carbonization, and its catalytic effect can increase reactivity. A water cooling method may cause reoxidation of metallic iron and therefore cannot be employed for the production of carbon iron composite.
As described above, chamber coke ovens constructed of silica stone bricks are difficult to use in the production of carbon iron composite. It is therefore desirable to use a vertical carbonization furnace having multiple tuyeres using the same type of gas as in formed coke as a heating medium, for example, a vertical shaft furnace constructed of chamotte bricks. However, considering the use of a vertical continuous carbonization furnace having a cooling function, a conventional carbonization furnace for formed coke requires gas removal at some point of the furnace which makes the equipment complicated. Furthermore, carbon iron composite requires the reduction of an iron-containing substance. Thus, a conventional method for producing formed coke cannot be directly used for carbon iron composite. The operational specifications such as gas distribution in tuyeres must be reconsidered. Furthermore, energy conservation cannot be avoided in future iron-manufacturing processes, necessitating a design concept of minimizing energy required for the production of carbon iron composite.
Accordingly, it could be helpful to provide a method and an apparatus for producing carbon iron composite in which production of metallurgical carbon iron composite with a vertical carbonization furnace can be performed with simplified equipment with decreased energy consumption.